What's the most fuel efficient engine speed?

[allgonepetetong]

I was driving home on Sunday morning after stayin with friends, and the petrol guage was a little lwer than I had anticipated. I had 65 miles to drive on the M40 and M25 and the trip computer was showing I had 80 miles range.

This should be fine but I know the trip computer undereads massively for MPG so I thought I would set the cruise at 65 to ensure i could get home without running out of fuel.

This got me thinking, what would be the most fuel economical speed / engine RPM to travel at?

I'm thinking that peak torque would be most efficient, but this it at 4500rpm in my car and in top that's around 90mph. I could cruise in 5th at around 75mph but that's defeating the point as I would be travelling for 8 more minutes and burning fuel all that time.

So, is top gear at peak torque really my most eficient (90mph) cruising speed?

[allgonepetetong]

Dracoro said:

In general, as low a speed as possible but above the speed where the engine would labour.

As for the peak torque bks, that would mean me driving around at 7500rpm all the time

There two things going on here though, are you asking which is the best for mpg or which is the most efficient (i.e. best performance per unit of fuel used etc.).

I'm actually asking what is the speed at which the greatest distance will be covered per unit of fuel. I had thought that this would be directly related to engine RPM so based me question there originaly.

Edited by allgonepetetong on Monday 7th November 13:20

[allgonepetetong]

Were getting a bit OT with engine effiency.

My question is, what is the most efficient speed at which to cruise? (speed at which greatest distance travelled per unit of fuel)

[allgonepetetong]

thinfourth2 said:

Zero rpm

Wouldn't be covering much distance though.

For those that believe this to be car specific, mine is a Maserati 4200. A reasonably slippery shape, 6 speed box, 4.2 V8.